Device for picture taking in low light and connectable to a mobile telephone type device

ABSTRACT

A picture taking device includes a power supply and a sensor of resolution higher than thirteen megapixels and an objective lens open at minimum to f/2.0 for at least one focal length value. A diagonal dimension of the photosensitive surface of the sensor is greater than 15 mm. A digital processor to reduce noise while preserving the textures in at least one image captured by the sensor. A picture taking method is provided using the picture taking device.

RELATED APPLICATION

The present application is a divisional of application Ser. No.14/909,115 filed Jan. 30, 2016, which is a §371 application fromPCT/EP2014/066346 filed Jul. 30, 2014, which claims priority from FrenchPatent Application No. 13 57575 filed Jul. 31, 2013, each of which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of electronics andphotography.

The present invention relates more specifically to a picture takingdevice which can be connected to a mobile phone or to a digital tablet.

In the remainder of the document, the term “tablet” will be used todenote a digital tablet comprising a processor and a touchscreen. Anexample of such a tablet is an IPAD® (registered trademark of AppleInc.) marketed by the Apple Inc., or alternatively the SAMSUNG GALAXYTAB® 2 (registered trademark of Samsung Electronics Co., Ltd.) marketedby the Samsung Electronics Co., Ltd.

The device according to the present invention has a picture takingquality equal to the quality of reflex or D-SLR (Digital Single LensReflex) type cameras, particularly in low lighting or very low lightingsituations. The device according to the present invention is verycompact (it fits into a pocket of a garment so that it is always readilyavailable) and is lightweight. The device according to the invention canbe attached by a rigid connector to a mobile phone or to a tablet so asto use the screen thereof by using one or two hands to hold thecombination of the phone or tablet and the device according to thepresent invention. It also offers additional features, such as a largedepth of field for example.

BACKGROUND OF THE INVENTION

The capture of well exposed images (elements with reflectance at 18% ofthe scene reaching the middle of the dynamic range in the capturedvisible image) in very low lighting situations in theory requires theuse either of an additional source of light of the flash type, whichchanges the ambiance of the scene, or of photographic equipment equippedwith a highly sensitive sensor and with a wide aperture objective lensso as to capture the maximum amount of light which is too bulky to fitinto a pocket of a garment.

In both instances, this is supposed to allow the use of an exposure timethat is short enough that it limits the movement blur in the image. Thegenerally accepted rule for defining the maximum exposure time T thatcan be used as a function of the 35 mm equivalent focal length value fis T=1/f (Xiao, F. Pincenti J., John G. and Johnson K., “Camera motionand mobile imaging”, Proceeding of Electronic Imaging (2007)).

The 35 mm equivalent focal length value currently considered as areference for fixed focus equipment is between 28 mm and 35 mm. Themaximum useable exposure time is therefore between 1/28s and 1/35s.

The use of an additional source of light is usually unwelcome because itchanges the low-lighting atmosphere of the scene and therefore does notallow the scene being experienced by the individual taking the photo tobe recreated.

Photographic equipment equipped with a highly sensitive sensor and witha wide aperture objective lens generally means a reflex camera withinterchangeable objective lens.

This type of equipment makes it possible to obtain very high qualityimages with low noise (high signal to noise ratio (SNR)), a high levelof sharpness and texture (high SFR (spatial frequency response) edge andSFR texture values) and a very broad dynamic range.

The noise as used in calculating the SNR can be characterized asmeasured from the “visual noise” described in D. Baxter, F. Cao, H.Eliasson, J. Phillips. Development of I3A CPIQ spatial metrics. SPIEConference on Electronic Imaging 2012. This evaluation of the noiseallows the variations in luminance and in chrominance in the image to betaken into consideration simultaneously.

The SFR edge and the SFR texture are two measurements of sharpness andof texture. These two measurements are described in the same documentunder the headings “Edge acutance” and “Texture blur” respectively.

Nevertheless, this type of equipment is heavy and cumbersome, whichmeans that it is not always possible to have it about one's person underall circumstances.

Moreover, the use of a very wide aperture combined with the use of alarge sized sensor results in a reduced depth of field, something whichon the one hand makes focusing more difficult and on the other handreduces the number of sharp elements in the image.

Photographic equipment of the reflex camera or DSLR camera type is knownin the prior art. This type of equipment has the disadvantage of beingbulky and heavy. DSLR cameras make it possible to obtain an excellentquality of image (very good SNR, and very good texture levels) becauseof the large size of their sensor (diagonals greater than or equal to 22mm) and the possibility of fitting them with objective lenses withapertures to f/2.0 or better. However, their bulk and weight do notallow them always to be carried about one's person. Furthermore, formost people, their cost is prohibitive.

Photographic equipment incorporated into mobile phones or tablets isalso known in the prior art. Most mobile phones or tablets currently onsale now incorporate an image and video capture system. Because of theiruse, mobile phones or tablets are not very bulky, meaning that they canbe carried around everywhere in a pocket of a garment or of a bag.However, because of their compactness, the inbuilt camera also needs tobe small in size. The sensor is therefore small in size, its diagonalgenerally being less than 7 mm, and the optical system is small also,the aperture thereof being at most f/2.0. The small size of the sensormeans low sensitivity but a greater depth of field, all of this incomparison with a reflex or DSLR camera. Because the optical systemneeds to be small in size, its aperture will be small. The camera builtinto the phone or the tablet will therefore be all the less ablesatisfactorily to record very low lighting scenes. The exposure timeseen with this equipment is of the order of 1/15s under theseconditions. This is longer than the maximum time defined hereinabovethat will allow a photo to be taken without movement blur. By default,in low lighting situations, the phone or the tablet will therefore havea tendency to use a flash in order to capture an image without movementblur. In the case of high resolution video recording (HD 1080p videoformat or better), this 1/15s exposure time is not compatible with arefresh rate of at least 24 images per second.

Devices of the clip-on camera type are also known from the prior art.Before mobile phones were almost systematically fitted with cameras,some manufacturers offered external camera modules to be connected tothe phone. These modules incorporated an optical view finder, a VGAcamera and a flash. They allowed the camera functionality to be added tothe phone but did not allow pictures to be taken with very highresolution under low lighting conditions.

Devices of the action camera type, such as for example the devicesmarketed by GOPRO® (registered trademark of Gopro, Inc.), are also knownfrom the prior art. These devices are not intended to be carried aroundeverywhere as they are and are not intended to be connected rigidly to aphone or a tablet. Devices of the action camera type are devicesintended chiefly for making videos in so-called sports environments.They are designed to be used with a casing. They are not optimized forcapturing stationary images in high resolution under low lightingconditions. They are designed to operate remote from their controlscreen.

Devices of the surveillance camera type connected to a phone or to atablet via a wireless device are also known in the prior art. Thesedevices are intended to be left at a fixed location, the phone or thetablet being used only for remote monitoring. As they are not physicallyattached to the phone or to the tablet, they cannot be used hand-held.

Picture taking systems using matrix cameras are also known in the priorart. By way of example, mention may be made of the systems marketed bythe following companies: Lytro, Pelican, Raytrix and Toshiba. Thesesystems have significant disadvantages. For example, the Lytro systemshave a low-resolution output (1 MP or megapixel) and requirepost-capture processing in order to obtain a final image. The Pelicansystems have a plurality of (sixteen) low-resolution monochrome sensors.The Raytrix ones are very bulky and need to be connected to a computer.They have a moderate resolution (3 megapixels), very high cost and arenot widely available to the public. Finally, the Toshiba systems aremainly designed for detecting distance (3D estimation) and are notdesigned to output high-resolution images.

SUMMARY OF THE INVENTION

The problem addressed by the present invention is therefore that ofcreating a picture taking device which under very low lightingconditions provides a high resolution (13 Mpix or more) visible image,an image quality similar to or better than that obtained through the useof interchangeable objective lens reflex (D-SLR) cameras, while at thesame time being small in bulk and weight, allowing it for example to fitinto a pocket (of a garment or of a bag). The device also provides,under very low lighting conditions, video of high resolution (HD 1080pvideo format or superior) with a refresh rate greater than or equal to30 images per second and with an image quality similar to or better thanthat obtained through the use of interchangeable objective lens reflex(D-SLR) cameras, while at the same time being smaller in bulk and inweight.

Within the meaning of the present invention, a low-lighting environmentis understood to be scene lighting of below 10 lux.

Within the meaning of the present invention, a raw image is the namegiven to an image derived from a sensor prior to the demosaicingoperation and prior to the application of a color matrix and tone curve.A raw image is made up of pixels of different colors and may be in theBayer format (for example green and red pixels alternating on theeven-numbered rows, with blue and green pixels alternating on theodd-numbered rows) or some other format (for example other combinationsof white and/or green and/or red and/or blue pixels). In one alternativeform, a raw image is made up of several, notably four, raw images takenconsecutively, or a video sequence made up of a series of raw images.

Within the meaning of the invention, a visible image is the name givento a color image (using the YUV, RGB or other coding standard, which mayor may not be compressed). A visible image is obtained by the digitalprocessing of a raw image and comprises, at minimum, the operations ofdemosaicing and application of a color matrix and tone curve.

The digital processing of a raw image in order to obtain a visible imagegenerally involves all or some of the following steps:

-   -   blackening    -   correction of defective pixels    -   calculation of statistics and estimation of exposure, white        balance and autofocus    -   correction of the vignetting and colored vignetting    -   correction of white balance    -   reduction of noise by spatial filtering on a raw image    -   reduction of noise by temporal filtering on raw images    -   demosaicing    -   color matrix    -   tone curve    -   YUV matrix    -   sharpness filter    -   colored fringe reduction filter    -   reduction of noise by spatial filtering on a visible image    -   reduction of noise by temporal filtering on visible images    -   increase of dynamic range by compositing differently exposed        images    -   increase of contrast by local contrast algorithm (local tone        mapping).

These steps are known to those skilled in the art and notably describedin Robert D. Fiete, “Modeling the Imaging Chain of Digital Cameras”,SPIE Tutorial Text Vol. TT92.

There is a desire to create a device which has a dynamic range of atleast 12 Ev, namely which is at least the equal to that of D-SLRdevices.

One of the objects of the present invention is also to create a picturetaking device which also by default has a deep depth of field thanks tothe use of image processing that makes it possible to reduce the size ofthe sensor and thus increase the depth of field for a given aperture, agiven captured-scene illumination and a given image quality.

The following parameters have been taken into consideration whendesigning the device according to the present invention:

-   -   L: quantity of light needed to illuminate the scene;    -   D: dimensions; and    -   C: cost.

In the context of the present invention, the desire is to maximizeparameter L and to minimize parameters D and C.

To this end, in its widest accepted sense, the present invention relatesto a picture taking device, characterized in that it comprises a sensorof resolution higher than thirteen megapixels, a diagonal of thephotosensitive surface of the sensor greater than 15 mm, in that itcomprises an objective lens open at minimum to f/2.0 for at least onefocal length value, in that it has digital processing means for reducingnoise while preserving the textures in at least one image captured bysaid sensor, in that it is able to be connected by a rigid connector toa device of the mobile phone or tablet type comprising a screen, in thatit has its own power supply means, and in that it has dimensions meetingthe following criteria: when the picture taking device is not connectedto a device of the mobile phone or tablet type, the maximum of theheight, of the width and of the depth of the smallest rectangularparallelepiped inside which the device can be inscribed is less than 70mm, the minimum of these same height, width and depth being less than 30mm, the volume of said device being less than 86 000 mm³, and in that itcomprises means for communicating images and/or commands with saiddevice of the mobile phone or tablet type.

Thus, the picture taking device according to the present invention has ahigh image quality under low lighting conditions: on the capturedsubject, with a mean exposure in the final dynamic range, and withdetails and textures preserved and a low noise level.

Because of its higher aperture objective lens and its sensor which ismore sensitive than the objective lens and the sensor of said device ofthe mobile phone or tablet type, and on account of the onboard imageprocessing, the picture taking device has light sensitivity that issuperior to that of said device of the mobile phone or tablet type.

Advantageously, the device comprises means implemented autonomouslyand/or in combination with means incorporated into said mobile phone orsaid tablet which in order to produce a visible image of at leastthirteen megapixels, is exposed in such a way as to have elements ofwhich the reflectance is 18% in the scene to be captured which reach themiddle of the dynamic range in the visible image with an SNR (signal tonoise ratio) midway through the dynamic range equal to or greater than34 dB, SFR edge and SFR texture values which differ by less than 10% andwhich, at one quarter of the Nyquist frequency, are less than or equalto 120% and which, at half the Nyquist frequency, are greater than orequal to 50%, from a capture of images for exposure times of 1/30s orless of a scene illuminated with light at a lighting level less than orequal to 10 lux.

These means allow the device according to the present invention torecord a high resolution video (in the HD 1080p video format orsuperior) with a refresh rate greater than or equal to thirty images persecond for a scene illuminated with ten lux or less, in which video eachframe is exposed in such a way as to have elements of which thereflectance is 18% in the scene that is to be recorded which reach halfthe dynamic range in the video recording, with an SNR midway through thedynamic range of 34 dB or better, SFR edge and SFR texture values whichdiffer by less than 10% and which, at one quarter of the Nyquistfrequency, are less than or equal to 120% and which, at half the Nyquistfrequency, are greater than or equal to 50%.

For preference, the picture taking device has no screen to allow thepreviewing or post-viewing of an image.

The absence of a screen means that the size and cost of the device canbe kept down.

According to one embodiment, said means for communicating images and/orcommands with said device of the mobile phone or tablet type allow animage taken by said picture taking device to be previewed on the screenof said device of the mobile phone or tablet type.

Advantageously, said means for communicating images and/or commands withsaid device of the mobile phone or tablet type allow said picture takingdevice to be controlled using the screen of said device of mobile phoneor tablet type.

For preference, said means for communicating images and/or commands withsaid device of mobile phone or tablet type allow parameters of saidpicture taking device to be set using the screen of said device ofmobile phone or tablet type.

For preference, said digital processing means for reducing noise whilepreserving the textures use a temporal merger of N images, N being anatural integer greater than or equal to two.

According to one embodiment, said digital processing means for reducingnoise while preserving the textures are hosted remotely on the device ofmobile phone or tablet type.

According to one alternative form, said device further comprises meansfor recording raw images in addition to or in place of the recording ofthe visible images after digital processing operations have beenperformed.

According to one embodiment, said rigid connector of said picture takingdevice is positioned in a hinge allowing its orientation relative tosaid device to change.

For preference, said picture taking device comprises image processingmeans allowing digital image stabilization.

According to one alternative form, said picture taking device employs anautofocus function to maximize the sharpness of the subject beingphotographed and/or filmed.

According to one embodiment, the autofocus function operatescontinuously so as to keep the subject of interest permanently in focus.

This makes it possible to reduce the latency during the taking of thepicture.

According to one embodiment, said device has a button to start therecording.

The button is used to start the taking of the picture or initiate thestart of the video recording.

According to one embodiment, the axis along which the button to startthe recording is pressed is situated in the plane containing the axis ofthe rigid connector and the points of the device that are used forholding same.

According to one embodiment, it is made up of two parts sliding one onthe other so as to obtain an open position and a closed position, saidclosed position allowing the connector and/or said button to start therecording to be protected, and said open position allowing access to theconnector and/or to said button to start the recording.

According to one embodiment, said button to start the recording has twomodes of operation: partially depressed and fully depressed.

The partially depressed mode makes it possible for example to lock theexposure and/or white balance and/or focusing parameters onto thecurrent values. It may also allow toggling from a low-consumptionpreview mode in which the image is undersampled to a full-resolutionimage acquisition mode allowing noise reduction digital processing to becarried out while at the same time preserving the textures using atemporal merger of N images, N being a natural integer greater than orequal to 2.

Advantageously, said connector is protected by a removable cap.

According to one embodiment, said device comprises means fortransmitting at least one raw image to said device of mobile phone ortablet type in at least one mode of operation.

The present invention also relates to a picture taking method using thepicture taking device described above, comprising a step of capturing at1/30s or under a scene comprising lighting of 10 lux or below, and astep of producing a visible image of a quality higher than thirteenmegapixels, said image being exposed in such a way as to have elementsof which the reflectance is 18% in the scene that is to be capturedwhich reach the middle of the dynamic range, with an SNR midway throughthe dynamic range of 35.5 dB or higher, SFR edge and SFR texture valueswhich differ by less than 10% and which, at a quarter of the Nyquistfrequency, are less than or equal to 120% and which, at half the Nyquistfrequency, are greater than or equal to 50%.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with the aid of the description,given hereinafter purely by way of explanation, of one embodiment of theinvention, with reference to the figures in which:

FIG. 1 illustrates the picture taking device according to the presentinvention, in an embodiment;

FIG. 2A depicts the picture taking device according to the presentinvention connected to a device of mobile phone type, in one embodiment;

FIG. 2B depicts the picture taking device according to the presentinvention connected to a device of digital tablet type, in oneembodiment;

FIG. 3 is a graph illustrating the signal to noise ratio midway throughthe dynamic range as a function of light for the picture taking deviceaccording to the present invention and for current mobile phones;

FIG. 4 depicts the picture taking device according to the presentinvention in an embodiment connected to a device of the IPHONE® type(registered trademark of Apple Inc.) via a connector of the “lightning”type;

FIG. 5 illustrates the picture taking device according to the presentinvention in an embodiment connected to a mobile phone via a connectorof the micro USB type;

FIG. 6 depicts the connector of the picture taking device according tothe present invention in a hinge system;

FIG. 7A depicts the picture taking device according to the presentinvention in an embodiment in the form of a closed pebble;

FIG. 7B depicts the picture taking device according to the presentinvention in an embodiment in the form of an open pebble;

FIG. 8A illustrates the picture taking device according to the presentinvention in an embodiment in the form of a closed cylinder;

FIG. 8B illustrates the picture taking device according to the presentinvention in an embodiment in the form of an open cylinder;

FIG. 9 depicts the picture taking device according to the presentinvention connected to a device of the mobile phone type, in oneembodiment;

FIG. 10 depicts an exploded view of one embodiment of the picture takingdevice according to the present invention comprising an objective lens,a sensor in a camera module 25×25×25 mm, a printed circuit containingthe digital processing, a battery and a connector;

FIG. 11 illustrates the picture taking device according to the presentinvention in one embodiment, being held by a person in their hand;

FIGS. 12A and 12B illustrate, according to one embodiment, the fact thatthe axis along which the button to start recording is pressed issituated in the plane containing the axis of the rigid connector and thepoints of the device that are used for holding same;

FIG. 13 illustrates an embodiment in which the device is in two partswhich slide one on the other thus generating two positions, an openposition and a closed position;

FIG. 14 illustrates an embodiment in which the device is provided with aremovable cap to protect the connector;

FIG. 15 illustrates an embodiment in which the rigid connector ispositioned in a hinge within the picture taking device according to thepresent invention; and

FIG. 16 depicts a previewing of the scene on the screen of the device ofmobile phone type.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates the picture taking device 10 according to the presentinvention, in one embodiment.

This device comprises a sensor 11 with resolution higher than thirteenmegapixels, a diagonal of the photosensitive surface of the sensorgreater than 15 mm, is able to be connected by a rigid connector 15 to adevice 20 of the mobile phone or tablet type comprising a screen 21. Thepicture taking device 10 according to the present invention furthermorehas its own power supply means 12, and comprises means 13 forcommunicating images and/or commands to said device 20 of mobile phoneor tablet type. Finally, the picture taking device 10 according to thepresent invention has an objective lens 16 open at minimum to f/2.0 forat least one focal length value.

According to one embodiment, said objective lens of said device 10 has afixed focal length.

Advantageously, the focal length allows at least the same field coverageas a 35 mm focal length on a 24×36 sensor. For a sensor with a diagonalmeasurement of 15 mm, that corresponds to a focal length of 12 mm.

According to another embodiment, said objective lens of said device 10is a zoom lens the shortest focal length of which is 12 mm or less andwhich is open at minimum of f/2.0 for this focal length.

FIG. 1 also illustrates the fact that the picture taking device 10according to the present invention comprises digital processing means 14for reducing the noise while preserving the textures.

The digital processing means for reducing the noise while preserving thetextures may be of the non-local mean calculation type as described inA. Buades, B. Coll and J. Morel (2005b), ‘A review of image denoisingalgorithms, with a new one’, Multiscale Model. Simul. 4, 490-530 or inA. Buades, B. Coll and J. Morel (2008b), ‘Nonlocal image and moviedenoising’, Internat. J. Computer Vision 76, 123-139 or of the“block-matching 3D” calculation type as described in K. Dabov, A. Foi,V. Katkovnik and K. Egiazarian (2007), ‘Image denoising by sparse 3Dtransform-domain collaborative filtering’, IEEE Trans. Image Processing16, 2080-2095 or in K. Dabov, A. Foi, V. Katkovnik and K. Egiazarian(2009), BM3D image denoising with shape-adaptive principal componentanalysis. In Proc. Workshop on Signal Processing With Adaptive SparseStructured Representations: SPARS 09, volume 49.

The digital processing means for reducing noise while preserving thetextures may incorporate a temporal merger of N images, N being anatural integer greater than or equal to two, which temporal merger isas described in Y. S. Moon, S. H. Lee, “A new fusion-based low lightstill-shot stabilization”, Conference on Multimedia Content and MobileDevices, Electronic Imaging 2013. The merger of N images allows a gainVN in stops. 3 dB is gained in SNR for each stop gained. Thus, accordingto an embodiment using a temporal merger of N=4 images and a sensor witha sensitive surface diagonal measurement of 16 mm provides a gain of 6dB, making it possible to reduce the size of the device according to theinvention. Indeed, the sensitivity is then the equivalent of that of asensor with a diagonal measurement of around 32 mm (namely a sensor andan objective lens which are 2 times larger in the x and y dimensions)which would need an objective lens with a focal length 2 times longer inorder to obtain the same field (namely 2 times greater in the zdirection): in order to obtain the same performance under low light, theoptical module (sensor+objective lens) would be bulkier by a factor ofaround 8 (approximately 128 cm³ rather than 16 cm³) for the samesensitivity, and would not allow the device to fit in a pocket.

Advantageously, the temporal merger uses what is known as an “antighost”mechanism that makes it possible to discriminate between the imageselements which are different and thus avoid merging them. The temporalmerger may be performed on the images before demosaicing or afterdemosaicing.

According to one embodiment, any image (picture or individual frame ofthe video recording) output by the device 10 is the resultant of themerger of the N images by the image processing means 14.

According to one embodiment, said digital processing means for reducingthe noise while preserving the textures are hosted remotely at least inpart on the device of mobile phone or tablet type. In this embodiment,the preview digital processing (display of video prior to the picturetaking for view finding) and the digital processing of the video for thevideo recording is performed in the device. In this embodiment, thestill image processing is performed as follows. For preference, one ormore successive raw images are transferred to the mobile phone or tabletwhich converts the raw image into a visible image involving noisereduction processing, for example temporal merger of several imagesand/or spatial noise reduction with the preservation of texture.

As an alternative, a preprocessing operation is performed in the device,for example a conversion of raw image to visible image of at least twoimages, and a post-processing operation of reducing the noise isperformed in the phone or the tablet, for example a temporal merger ofseveral images and/or a spatial denoising with the preservation oftexture.

As an alternative, one or more successive raw or visible images aretransferred to a personal computer or server which carries out a noisereduction processing operation and the conversion of the raw image tothe visible image where appropriate.

The noise reduction processing may be carried out automatically withparameters that are predetermined as a function of the sensor gain, orthat take account of user settings (denoising level, white balance,contrast, etc).

The processing in the phone or in the tablet may be carried out bysoftware on the main processor and/or by software on the graphicprocessor and/or by using a component comprising wired or programmablecalculation means suited to image processing.

In an alternative form, said device allows the raw images to be recordedin addition to or in place of the recording of the visible images thathave undergone digital processing. The user of the device will then beable to apply the digital processing of his choice to the recorded rawimages. He will for example be able to apply a merger involving moreimages than that applied in the device.

The figures also illustrate the fact that, in one embodiment, thepicture taking device 10 according to the present invention comprises abutton 17 to start the recording.

The picture taking device 10 according to the present invention hasdimensions meeting the following criteria: the maximum of the height, ofthe width and of the depth of the smallest rectangular parallelepipedinside which said device 10 can be inscribed must be less than 70 mm,the minimum of these same height, width and depth must be less than 30mm, the volume of the device is less than 86 000 mm³. Thus, it easilyfits into the pocket of a bag or of a garment. This allows the useralways to have about his person a picture taking device of digitalreflex camera quality allowing pictures to be taken under very lowlighting conditions, which can be used in particular for indoorphotographs or moving scenes, notably of children. It is possible withinthis volume and with these dimensions, for example as depicted in FIG.12, to house a sensor with sensitive surface diagonal of 16 mm, anobjective lens open to f/2.0 the 35 mm equivalent focal length of whichis 28 mm (approximately 8 cm³ for the optic module combining the sensorand the objective lens), electronics comprising digital processing meansthat reduce noise while preserving the textures and communication meansaccording to the invention (approximately 10 cm³ for the electronics), abattery (approximately 15 cm³ for 5 Wh using lithium-polymertechnology), a rigid connector (approximately 1 cm³ with the hingedevice) and mechanics (approximately 10 cm³).

FIG. 2A depicts the picture taking device 10 according to the presentinvention connected to a device 20 of the mobile phone type, in oneembodiment. FIG. 2B depicts the picture taking device 10 according tothe present invention connected to a device 20 of the digital tablettype, in one embodiment. This device 20 of the mobile phone or tablettype comprises a screen 21. The picture taking device 10 according tothe present invention according to the present invention is connectedrigidly to said device 20 of the mobile phone or tablet type: this isnot a connection using a flexible cable but rather a wireless connectionof the Bluetooth, Wi-Fi or NFC type.

The rigid connection may adopt a number of forms:

-   -   a fixed connector fixed to the device according to the invention        and that plugs into the corresponding connector belonging to the        phone or tablet, and/or    -   a fixed connector fixed to the device according to the invention        and able to rotate so that the camera can be aimed in an        adjustable direction by the user and that plugs into the        corresponding connector belonging to the phone or to the tablet,        and/or    -   a mechanical attachment for example using clips    -   it being possible for the connector to be a USB, micro USB,        lightning or some other form of connector    -   the connector allowing images to pass to the phone or the tablet        during the previewing phase (display of video before the taking        of pictures allowing view finding), and/or during the video        recording and/or after still images have been captured, and/or        allowing commands to pass from the phone or from the tablet to        the device according to the invention.

The rigid connection 15 allows the picture taking device 10/device 20 ofthe mobile phone or tablet type assembly to be held in one hand, holdingthe device 20 of the mobile phone or tablet type. The rigid connectionallows the picture taking device 10 and device 20 of the mobile phone ortablet type to be held in two hands: one hand to hold the device 20 ofmobile phone or tablet type and one hand to press the picture takingbutton 17 of the picture taking device 10. Without this rigidconnection, it would be very difficult to view find and take picturesusing the camera in one hand and the phone or tablet in the other.

FIG. 11 illustrates the picture taking device according to the presentinvention in this embodiment, held by a person in their hand.

The rigid connection allows the device according to the invention andthe phone or tablet to be secured together mechanically and also allowsthe passage of the electrical signals required for:

-   -   transmitting images from the device according to the invention        to the phone or tablet for previewing the images on the screen        of the phone or of the tablet, it being possible for these        images to be compressed and decompressed on the fly so as to        reduce the bit rate to a format compatible with the phone or        with the tablet, for example H264 or H265/CHVC or the like,        and/or    -   transmitting commands and/or controls from the phone or the        tablet to the device according to the invention, notably:        -   command to take a picture: taking a still image,            starting/stopping a video recording,        -   choice of resolution,        -   choice of exposure: aperture, exposure time, sensitivity of            the sensor, mode (priority on aperature, priority on            exposure time, priority on sensitivity, manual, automatic,            etc.)        -   setting of the white balance,        -   autofocus settings (deactivation, choice of area of            interest, etc.),        -   image stabilization settings,        -   choice of the type of scene: automatic, landscape, portrait,            etc.,        -   other camera settings, and/or    -   transmitting commands and/or controls from the device according        to the invention to the phone or the tablet, notably:        -   command to take a picture or other commands situated on the            device according to the invention and able to influence the            application of to the mobile phone or the tablet        -   data regarding the scene and calculated by the device            according to the invention and/or by the mobile phone or by            the tablet from statistics about the image which are            supplied by the device according to the invention to the            mobile phone or to the tablet, for example: illuminant            determined by the white balance, exposure (exposure time,            sensitivity, gain), underexposure alert, movement alert,            presence and position of faces, type of scene, etc.

According to one embodiment, the means 13 for communicating imagesand/or commands to said device 20 of the mobile phone or tablet typeallow an image taken by said picture taking device 10 to be previewed onthe screen 21 of said device 20 of mobile phone or tablet type. Thus,the user can enjoy the benefit of a large screen, even though the deviceaccording to the invention is small in size without a large screen andcan fit into a pocket.

FIG. 16 depicts a preview of the scene on the screen of the device ofmobile phone type.

In one embodiment, these means 13 allow said picture taking device 10 tobe controlled via the screen 21 of said device 20 of the mobile phone ortablet type. Thus, the user may enjoy the benefit of numerous commandsand settings, even though the device according to the invention is smallin size with a small number of buttons and can fit into a pocket.

In one embodiment, these means 13 allow parameters of said picturetaking device 10 to be set using the screen 21 of said device 20 of themobile phone or tablet type. Thus, the user can enjoy the benefit ofmultiple commands and settings, even though the device according to theinvention is small in size with a small number of buttons and can fitinto a pocket.

In one embodiment, the device 20 of the mobile phone or tablet type hasone of the following three operating systems: Android, iOS or WindowsPhone (registered trademarks). The means 13 of said picture takingdevice 10 according to the present invention for using the screen 21 ofsaid device 20 of mobile phone or tablet type have the ability tooperate with the three abovementioned mobile phone or tablet operatingsystems.

FIG. 3 is a graph illustrating the signal to noise ratio as a functionof light for the picture taking device according to the presentinvention and for present-day mobile phones or tablets for 1/30 secondexposure times.

The picture taking device 10 according to the present invention has ahigh image quality under low lighting conditions, and notably a reducednoise level when measured on a visible image exposed in such a way as tohave elements of which the reflectance is 18% in the scene that is to becaptured that reach the midway point of the dynamic range:

-   -   for a 100 lux scene, the signal to noise ratio (SNR) midway        through the dynamic range is of the order of 44 dB for the        picture taking device 10 according to the present invention, and        is of the order of 29 dB for present-day phones or tablets;    -   for a 25 lux scene, the signal to noise ratio is of the order of        38 dB for the picture taking device 10 according to the present        invention, and is of the order of 23 dB for present-day phones        or tablets; and    -   for a 10 lux scene, the signal to noise ratio is of the order of        34 dB for the picture taking device 10 according to the present        invention, and is of the order of 19 dB for present-day phones        or tablets.

The gain of 15 dB between the device and a present-day phone or tabletcan be broken down as follows:

-   -   the sensor is more sensitive: present-day phones or tablets use        sensors of which the diagonal of the photosensitive surface        measures less than 7 mm; the picture taking device 10 uses a        sensor of which the diagonal of the photosensitive surface        measures greater than 15 mm. For the same number of pixels        across the sensors, that represents a gain of the order of 9 dB.    -   digital processing for reducing noise while preserving the        texture involving the temporal merger of four images. The gain        is 2 stops, namely 6 dB.

In one embodiment, the objective lens comprises a diaphragm that allowsthe aperture of the objective lens, and, therefore, the depth of field,to be controlled when there is sufficient light.

The picture taking device according to the present invention in anembodiment in which it takes the form of a pebble. This shape slipseasily into a pocket.

The picture taking device according to the present invention in anembodiment in the form of a cylinder. This shape slips easily into apocket

FIG. 4 depicts the picture taking device according to the presentinvention in an embodiment connected to an iPhone (registered trademarkof the company Apple) device via a lightning type connector. Thelightning type connector is thus used in addition to its usualcommunications function as a rigid connector allowing the phone ortablet and the device according to the invention to be mechanicallyfixed together to make it easier to hold and take pictures as describedabove.

FIG. 5 illustrates the picture taking device according to the presentinvention in an embodiment connected to a phone or to a tablet operatingunder the Android operating system via a micro USB type connector. Themicro USB connector is thus used in addition to its usual communicationfunction as a rigid connector allowing the phone or the tablet and thedevice according to the invention to be mechanically fixed together tomake it easier to hold and take pictures as described above.

FIG. 6 depicts the connector of the picture taking device according tothe present invention in a hinge system. Thus, the user can enjoy thebenefit of an orientable screen making it possible for example to takepictures with his arms above the height of his face and aiminghorizontally, even though the device according to the invention is smallin size and can fit into a pocket.

FIG. 7A depicts the picture taking device according to the presentinvention in an embodiment in which it has the shape of a closed pebble.This shape slips easily into a pocket with the connector protected.

FIG. 7B depicts the picture taking device according to the presentinvention in an embodiment in the form of an open pebble. This shapeallows access to the connector for inserting it into the device 20 ofthe mobile phone or tablet type.

FIG. 8A illustrates the picture taking device according to the presentinvention in an embodiment in the form of a closed cylinder. This formslips easily into a pocket, with the connector protected.

FIG. 8B illustrates the picture taking device according to the presentinvention in an embodiment in the form of an open cylinder. This shapeallows access to the connector for inserting it into the device 20 ofmobile phone or tablet type.

FIG. 9 depicts the picture taking device according to the presentinvention connected to a device of mobile phone or tablet type, in oneembodiment. The device is thus easy to hold in the hands and allowspictures to be taken holding the assembly formed by the device accordingto the invention and the mobile phone or tablet firmly in order toreduce movement blur.

FIG. 10 depicts an exploded view of one embodiment of the picture takingdevice according to the present invention comprising an objective lens,a sensor in a camera module measuring 25×25×25 mm, a printed circuitcontaining the digital processing, a battery and a connector.

FIG. 12A and FIG. 12B illustrate, according to one embodiment, the factthat the axis along which the button for starting the recording 16 ispressed is situated in the plane containing the axis of the rigidconnector 15 and the points of the device 10 which are used for holdingit. The device is therefore easy to hold in the hand and allows picturesto be taken holding the assembly formed by the device according to theinvention and the mobile phone or tablet firmly in order to reducemovement blur.

FIG. 13 illustrates an embodiment in which the device is in two partswhich slide one on the other thus generating two positions, an openposition and a closed position. Said closed position allows theconnector 15 and the start button 16 to be protected. Said open positionallows access to the connector 15 and to the start button 16. Saidclosed position makes it possible to fall inside the dimensionconditions specified earlier.

FIG. 14 illustrates one embodiment in which the device is provided witha removable cap to protect the connector 15.

FIG. 15 illustrates an embodiment in which the rigid connector ispositioned in a hinge within the device 10. This hinge allows device 10to pivot about the connector and to change the orientation of the device10 with respect to the device 20 of mobile phone or tablet type. Thusthe user can enjoy the benefit of an orientable screen making itpossible for example to take pictures with his arms above the height ofhis face and aiming horizontally, even though the device according tothe invention is small in size and can fit into a pocket.

In one embodiment, the device 10 according to the present inventioncomprises means for producing a visible image of at least thirteenmegapixels exposed in such a way as to have elements of which thereflectance is 18% in the scene to be captured which reach the middle ofthe dynamic range in the visible image with an SNR in the middle of thedynamic range of 34 dB or higher, SFR edge and SFR texture values whichdiffer by less than 10% and which, at a quarter of the Nyquistfrequency, are less than or equal to 120% and which, at half the Nyquistfrequency, are greater than or equal to 50%, from the capturing ofimages at 1/30s or less of a scene illuminated at less than 10 lux. Inthis embodiment, said device 10 comprises an objective lens open tof/2.0 having an MTF at half the Nyquist frequency of more than 50%, asensor the diagonal of the photosensitive surface of which measures 15.8mm, for example the Aptina AR1411HS sensor, having no flash. It has abattery to power it, it being possible for example for the battery to berecharged depending on the embodiment using an external connector and/orby induction and/or by being removed from the device and/or via thephone or via the tablet. The digital processing means that reduce thenoise while preserving the textures are made up of a denoising algorithmas described in K. Dabov, A. Foi, V. Katkovnik and K. Egiazarian (2009),“BM3D image denoising with shape-adaptive principal component analysis”.In Proc. Workshop on Signal Processing With Adaptive Sparse StructuredRepresentations: SPARS 09, volume 49 and a temporal merger performed onfour images recorded consecutively by the sensor. Thus, the deviceaccording to the invention allows pictures to be taken in low lightingconditions while at the same time being small in size and fitting into apocket.

Advantageously, in this embodiment, the device 10 uses these means torecord a high-resolution (HD 1080p video format or better) video with arefresh rate greater than or equal to 30 images per second for a sceneilluminated with 10 lux or less, each frame of which video is exposed insuch a way as to have elements of which the reflectance is 18% in thescene that is to be recorded that reach the midway point of the dynamicrange in the video recording, with an SNR in the middle of the dynamicrange that is equal to or better than 34 dB, SFR edge and SFR texturevalues which differ by less than 10% and which, at a quarter of theNyquist frequency, are less than or equal to 120% and which, at half theNyquist frequency, are greater than or equal to 50%.

In one embodiment, said picture taking device 10 has no screen forpreviewing or post-viewing an image. That makes it possible to reducethe size of the device.

In one embodiment, said picture taking device 10 comprises imageprocessing means that allow digital image stabilization. This makes itpossible to reduce the size of the device by dispensing with the needfor a bulky optical stabilization device while at the same timeimproving the picture taking performance under low lighting conditionsand allowing a better temporal merger and thus noise reduction withbetter texture preservation performance.

In one embodiment, said picture taking device employs an autofocusfunction to maximize the sharpness of the subject being photographedand/or filmed. The autofocus function comprises a physical part thatperforms the operation of actually changing the focus and a system thatanalyses the quality of the focusing and that controls the physical partin order to optimize the focusing. The system that analyses and controlsthe optimizing of the focusing may for example be the one described inUS2006/0164934A1. Greenleaf, Allen R., Photographic Optics, TheMacMillan Company, New York, 1950, pp. 25-27 provides formulae forcalculating the distance Dp to the first plane of sharpness and thedistance Dd to the last plane of sharpness for a given optical systemand the optimal focusing distance:

${Dp} = \frac{s\left( {H - f} \right)}{H + s - {2f}}$${Dd} = \frac{s\left( {H - f} \right)}{H - s}$ where$H = {\frac{f^{2}}{Nc} + f}$f is the focal length of the objective lens.s is the distance at which the optical system is focused.N is the aperture of the optical system.c is the diameter of the confusion circle.

The depth of field Pc is the distance between the first plane ofsharpness and the last plane of sharpness:

${Pc} = \frac{2{s\left( {H - f} \right)}\left( {s - f} \right)}{\left( {H + s - {2f}} \right)\left( {H - s} \right)}$

In the context of the invention, the focal length will be greater than10 mm, the aperture f/2.0 or more, c less than or equal to 5.6 μm.

For an s value of 1 m, Dp equals 0.9 m, Dd equals 1.12 m and Pc equals0.22 m. In order to photograph or film subjects at other distances, achange in focus is needed. This focusing is performed by the autofocusfunction.

In one embodiment, said autofocus function operates continuously so asto keep the subject of interest permanently in focus. This makes itpossible to use an objective lens open to an aperture of more than f/2.0(with limited depth of field) thus improving performance under lowlighting conditions.

The invention is described in the foregoing by way of example. It mustbe understood that a person skilled in the art is capable of embodyingthe invention in various different ways without thereby departing fromthe scope of the patent.

The invention claimed is:
 1. A picture taking device comprising: asensor of resolution higher than thirteen megapixels, a diagonaldimension of a photosensitive surface of the sensor being greater than15 mm; an objective lens opening at minimum to f/2.0 for at least onefocal length value; a digital processor to reduce noise in at least oneimage captured by the sensor to provide a high resolution image greaterthan or equal to 13 Mpix without a movement blur under a low lightingcondition less than or equal to 10 lux; a power supply; and wherein thepicture taking device has dimensions meeting the following criteria toprovide a compact and lightweight picture taking device that fits into apocket of a garment: maximum and minimum of a height, a width and adepth of a smallest rectangular parallelepiped inside which the picturetaking device can be inscribed are less than 70 mm and less than 30 mm,respectively, and a volume of the picture taking device is less than86,000 mm³.
 2. The picture taking device as claimed in claim 1, whereinthe digital processor is configured to autonomously produce a visibleimage of at least thirteen megapixels, having an exposure configured tohave elements of which a reflectance is 18% in a scene to be capturedwhich reach the middle of a dynamic range in the visible image with asignal to noise ratio midway through the dynamic range equal to orgreater than 34 dB, spatial frequency response edge and spatialfrequency response texture values which differ by less than 10% andwhich, at one quarter of the Nyquist frequency, are less than or equalto 120% and which, at half the Nyquist frequency, are greater than orequal to 50%, from a capture of images for exposure times of 1/30s orless.
 3. The picture taking device as claimed in claim 1, wherein thedigital processor is configured to reduce the noise while preservingtextures by a temporal merger of N images, N being a natural integergreater than or equal to
 2. 4. The picture taking device as claimed inclaim 1, further comprising a recorder to record raw images in additionto or in place of a recording of visible images after digital processingoperations have been performed.
 5. The picture taking device as claimedin claim 1, further comprising an image processor to provide a digitalimage stabilization.
 6. The picture taking device as claimed in claim 1,further comprising an autofocus element to maximize a sharpness of asubject being photographed or filmed.
 7. The picture taking device asclaimed in claim 6, wherein the autofocus element operates continuouslyto keep the subject permanently in focus.
 8. The picture taking deviceas claimed in claim 1, further comprising a button to start a recording.9. The picture taking device as claimed in claim 8, wherein the buttonto start the recording has two modes of operation: partially depressedand fully depressed.
 10. A picture taking method, comprising the stepsof: capturing, at 1/30s or lower, a scene comprising lighting of 10 luxor below using a picture taking device comprising: a sensor ofresolution higher than thirteen megapixels, a diagonal dimension of aphotosensitive surface of the sensor being greater than 15 mm; anobjective lens opening at minimum to f/2.0 for at least one focal lengthvalue; a digital processor to reduce noise in at least one imagecaptured by the sensor to provide a high resolution image greater thanor equal to 13 Mpix without a movement blur under a low lightingcondition less than or equal to 10 lux; a power supply; and wherein thepicture taking device has dimensions meeting the following criteria toprovide a compact and lightweight picture taking device that fits into apocket of a garment: maximum and minimum of a height, a width and adepth of a smallest rectangular parallelepiped inside which the picturetaking device can be inscribed are less than 70 mm and less than 30 mm,respectively, and a volume of the picture taking device is less than86,000 mm³; and producing a visible image of a quality higher thanthirteen megapixels, the image having an exposure configured to haveelements of which the reflectance is 18% in the scene that is to becaptured which reach the middle of the dynamic range, with a signal tonoise ration midway through the dynamic range of 34 dB or higher, aspatial frequency response edge and spatial frequency response texturevalues which differ by less than 10% and which, at a quarter of theNyquist frequency, are less than or equal to 120% and which, at half theNyquist frequency, are greater than or equal to 50%.